Development of Techniques for Real‐Time Monitoring and Control in Plasma Etching: II . Multivariable Control System Analysis of Manipulated, Measured, and Performance Variables

Abstract

Process control strategies have been developed for reactive ion etching of silicon and silicon dioxide in and plasmas. Four measured variables, four manipulated variables, and seven performance variables were considered for both gas mixtures. Relative gain array analysis and singular value decomposition were used to select manipulated/ process variable control loop pairings for feedback control and to evaluate potential difficulties in control system performance. Singular value decomposition was also used to determine which process variable (measured real‐time) correlated best with a given performance variable. Block relative gain analysis of multivariable interactions in the process indicated that single loop feedback control would be inadequate for control of both and etching, which was subsequently verified by simulation. Multivariable control (partial decoupling) was much more effective in reducing dynamic fluctuations in the process variables.